5 Weeks Pregnant: The Week the Heart Starts to Beat

Last week, you saw the line. This week, your baby grows a heart, and it starts to beat.

Week five is one of the most staggering weeks of the whole pregnancy, and nearly all of it happens in secret. In the space of just a few days, deep inside you, your baby lays down the very first thread of its brain and spine. And by the end of the week, a tiny tube of cells does something it will not stop doing for as long as your baby lives. It begins to beat. A brand new heart, keeping its own quiet time inside you, while you go about your day feeling almost nothing at all.

Your baby's brain and spine begin to form

This is the week the neural tube forms, and it is one of the quiet wonders of the whole pregnancy.

It begins as a flat little ribbon of cells laid along your baby's back. Then, almost too neatly to believe, the ribbon lifts at its edges and folds in on itself, zipping closed into a tube. It even starts sealing in the middle and works toward both ends at once, like a zip doing itself up in two directions. That single tube is the beginning of your baby's entire brain and spinal cord. Every thought your baby will ever have, every wiggle of a finger, every dream and every word, all of it begins as this one folding seam, this week.

And this is exactly why folate matters so much, right now. It is the closing of this very tube that folate helps protect. So if you have been taking it, this is the quiet work it has been doing all along. And if you have only just started, please hear this clearly. You have not missed your chance. The tube is still forming this week, so getting folate on board today genuinely helps. Most women only begin once they find out they are pregnant, which is exactly where so many of you are right now, so wherever you are starting from, you are in good company. We talked all about folate, and the two different kinds, back in week one.

And then, the very first heartbeat

By the end of this week, something happens that I have watched on countless monitors and still cannot quite believe.

Your baby's heart, still just a simple tube of cells with no chambers and barely any shape, gives a first twitch. Then another. And then it finds a rhythm, around a hundred to a hundred and ten beats a minute, much faster than your own, pushing the first faint traces of blood through a body only a few millimetres long.

Here is the part that gets me every single time. The heart is the very first organ your baby ever puts to work. It starts beating before it has chambers, before there are lungs to fill, before there is a face, and long before the brain that will one day steer it is anything more than that folding seam. Everything else about your baby is still the roughest sketch. But the heart does not wait for any of it. It simply begins. And from this week on, it will not stop, not once, not for a single second, for the whole of your baby's life.

Right now, as you read this, it is beating. You cannot feel it. It is far too soon to hear it. And still it goes, faithfully, in the dark, counting out the very first minutes of a life that is already on its way to you.

Three thin layers, one whole human

It is worth pausing on how your baby is built right now, because it is so elegant.

Your baby is currently made of three fine layers of cells, and each layer has been handed its own job. One layer will become the brain, the nerves, the skin and the senses. The middle layer will build the heart, the blood, the bones and the muscles. The inner layer will form the lungs and the gut.

Three simple sheets of cells, holding between them the plans for an entire person. The whole map of your baby is already drawn. Now it just has to build.

How big is my baby at 5 weeks?

Still tiny. Your baby is only around four millimetres long this week, curled into a soft C-shape like a little comma.

It looks nothing like a baby yet, more like a curl of pure possibility. And yet inside that curl, a heart is beating and a brain is taking shape. Size tells you almost nothing about what is really going on in there.

Is it normal to suddenly feel awful? Or to feel nothing?

Both, and this is often the week it tips one way or the other.

With hCG climbing fast now, this is when a lot of women meet their first real symptoms. A bone-deep tiredness. Sore, heavy breasts. The first waves of queasiness. A metallic taste, a nose that suddenly smells everything, tears that arrive from nowhere. If that is you, it is not a bad sign at all. It is usually just rising pregnancy hormones doing exactly what they are meant to.

And if you feel perfectly fine? That is also completely normal, and it does not mean anything is wrong. Symptoms, or the lack of them, are a wildly unreliable guide to how a pregnancy is going. Try not to read your whole morning by them.

From Courtney. There is a heart beating inside you right now, and you cannot feel a thing. I have stood beside a lot of monitors in my years as a nurse, and that idea still stops me in my tracks. Somewhere in the quiet of this ordinary week, while you make the tea and go to work and wonder if any of this is even real, a heart smaller than a grain of sand has started up and is keeping its own time, just for your baby. You do not have to do anything to earn it or to keep it going. It is simply happening, on its own, because your body and your baby already know exactly what they are doing. I hope that lets you breathe out, just a little.

The one thing to do this week

Take your folate. If you have not started yet, start today. And if you already have, keep going without fail. This week of all weeks, it earns its place.

The neural tube is forming right now, which is the exact window folate was made for. So whether you have been taking it for months or you start this very afternoon, it is doing real good. And please do not spend a single second on guilt about when you began, because the overwhelming majority of women start exactly when they find out, and the science is still on your side.

And if you have not yet booked that first appointment with your doctor or midwife, this is a lovely week to do it.

Coming up in week six

Next week, your baby starts to take shape in earnest. That brand new heartbeat grows stronger and steadier, and around now it may even be glimpsed for the first time on an early ultrasound. Tiny buds appear where the arms and legs will grow. And the first hints of a face begin to form, the places where the eyes, the ears and the mouth will be.

Your little comma is about to start looking a lot more like a baby. Week six is where it all begins to become visible. I will see you there.

Written by Courtney Garland, NICU nurse, lactation consultant and mother of four, and founder of The Mama Years. This is here to inform and reassure you. It is not a substitute for medical advice, so always follow the guidance of your own doctor or midwife.

The Mama Years. 2026.

References

Cleveland Clinic. (2023). Fetal development: Stages of growth. https://my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth

March of Dimes. (2023). Pregnancy week by week. https://www.marchofdimes.org/pregnancy-week-week

Mayo Clinic. (2025). Fetal development: The first trimester. https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-care/art-20045302

Merck Manual. (2024). Stages of fetal development (Consumer Version). https://www.merckmanuals.com/home/women-s-health-issues/normal-pregnancy/stages-of-fetal-development

The Mama Years is written by Courtney Garland, a NICU registered nurse and IBCLC lactation consultant, against the research. When the science is genuinely unsettled, she says so instead of guessing. Nothing here replaces the advice of the clinician looking after you.